YW (Yagi for Windows)

[Pages:31]YW (Yagi for Windows)

Version 2.0, March 16, 2006

Copyright ARRL, 2000-2006, by R. Dean Straw, N6BV

A Personal Note from N6BV

In the summer of 1959 I was first licensed as WH6DKD. Early on, I became greatly interested in HF antennas and in contesting. Over the last twenty years I have been fascinated with computer modeling of antennas, especially after having spent many, many hours wrestling with behemoth Yagi arrays while helping set up contest stations at W6OWQ and at N6RO in the early and mid 1980s, and after setting up and operating with stacked tribanders at my own contest station in New Hampshire during the 1990s.

For the last twenty years or so I have spent an inordinate amount of time "fooling with the computer," as my wife gently puts it. A number of people assisted at one time or another in these projects, whether they knew about it directly or not. The YW program is built upon the considerable body of work that has been done by other investigators, most of them considerably more capable theoreticians than I am. Notable among these have been Dr. I.L. Morris, Jim Lawson, W2PV, Stan Jaffin, WB3BGU, John Kenney, W1RR, Brian Beezley, K6STI, Wayne Hillenbrand, N2FB, and Dave Leeson, W6NL (ex-W6QHS). There have been others as well. I give thanks to them all.

THE YW PROGRAM

YW is designed to evaluate monoband Yagi antennas. It is fun to use, and it also is accurate when real-world antennas are built from it. YW results compare very closely with Brian Beezley's YO or YA programs and with NEC-based programs, such as EZNEC, NEC-Win Plus or NEC-4. YW is a special-purpose program, designed strictly for monoband Yagis. It has the advantage of running many times more quickly than general-purpose programs such as NEC but it has some attendant limitations.

YW evaluations over ground are done over flat "perfect" ground. Mutual impedances between Yagi elements and the ground are not specifically taken into account in YW, so calculations for antennas mounted less than approximately /8 above ground should be taken with a small grain of salt. Antennas mounted in the presence of other nearby antennas or mounted very low to the ground are the specialities of method-of-moment programs like NEC. Despite these caveats, YW will get you very close to a final design -- one where you can simply cut the elements and expect that your Yagi will work as advertised.

Version 2.0 of YW includes the ability to do polar plots. Version 2.0 also produces higher resolution charts in the main window than the original version. I use the flexible and very capable TeeChart Pro 5 graphing package in my Windows programs and I highly recommend this software to other programmers. See the Steema Web site for details: .

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Computer Requirements

The minimum requirements to run YW (and its companion Windows programs TLW, Transmission Line for Windows and HFTA, HF Terrain Assessment) are a PC running Windows 95 or later, including Windows 98, 98SE, XP and Windows 2000. The processor should be at least a Pentium 90 MHz, with at least VGA 640 ? 480 screen resolution (with "Small" font size), 24 MB of RAM (32 MB for Windows 2000) and a CD-ROM. Note that a screen resolution of 800 ? 600 or even better yet, 1024 ? 768, will result in easier-to-read windows. These higher resolutions are best viewed with "Large" font size.

To set the screen size from the Windows Desktop Taskbar, select Start, then Settings, Control Panel, Display and then click on the Settings tab. Choose either 800 ? 600 or 1024 ? 768 in the Screen Area list box. Next, click on the Advanced button and select "Large Fonts" in the Font Size list box. Then reboot your computer (if necessary) and exit by clicking on the OK buttons until you can exit the Control Panel folder.

Installing YW

Normally, you would automatically install YW when you use ABSETUP to install the other programs from the CD-ROM included with the 20th Edition of The ARRL Antenna Book. This section describes how to re-install YW, or install it for the first time if you opted not to install it previously.

At the lower left-hand of your Desktop, click on Start, then Run. Click on the Browse button and then select the drive corresponding to your CD-ROM. We'll assume here that it is drive D. Select the ABSETUP program by clicking on it twice and then clicking OK. Follow the on-screen instructions to enter your name and company, then choose your target directory (the default is c:\AntBk20) and then Program Group. When the menu tree "Select Components to Install" appears, deselect everything except for YW. Then click OK to start the installation. Afterwards, allow the computer to shut down and reboot.

Possible Problems During YW Installation

You may possibly encounter warnings or problems during installation or re-installation of YW. The program uses DLLs (Dynamic Linked Libraries) and other files (such as OCX ActiveX Controls) supplied from Microsoft for Visual Basic 6, the language in which YW was written. In addition, there is a DLL supplied by Compaq for Compaq Visual Fortran, the core mathematical code for the Yagi modeling. Microsoft and Compaq will occasionally update their DLLs and OCXs.

If the installation program finds an older file that must be updated, it will ask your permission to do so. It is OK to allow the program to do the updating, since older programs that also use these DLLs and OCXs should still work--in other words, they are backwards compatible. On rare occasions, however, a newer DLL or OCX will not function with older programs. Should this occur, please contact the publisher of the other program, or contact ARRL for problems with YW, using the e-mail address at the end of this document.

We have found that some auxiliary "Uninstall" programs can interact with an installation or re-installation of YW because certain uninstall programs automatically makes DLLs and OCXs "read-only." Consult your operator's manual for such uninstall programs if you see a warning

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message about a "read-only" file during YW installation. You will probably have to Cancel your YW installation and run the auxiliary uninstall program to update its file inventory. Then you can run the YW installation again.

TAKING YW FOR A TEST DRIVE From the Desktop Taskbar at the lower left-hand corner of the screen, select Start, then Programs, followed by clicking on YW. You will now see the YW icon to the right. You could start YW immediately by left-clicking on the YW icon if you like. At this point, however, you could also create an shortcut icon on your Desktop in Windows 98 or higher by right-clicking on the YW icon and choosing Create Shortcut. This creates a shortcut, which you may select by right-clicking on it, dragging it onto your Desktop and then selecting Move Here. If you wish, you can use the same procedure to create a shortcut on your Desktop for the entire Program Group (by default called "Antenna Book Software") containing all the icons for the Antenna Book programs.

Fig 1--A typical YW main screen.

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Tool Tips and Selecting a New Yagi File Let's assume you have started the program. YW starts out with a bold red command: "Open a new file to start." This is asking for the filename of the disk file you wish to analyze. First, however, move the mouse cursor so that it hovers over the Open button. After a short time, a "tool tip" will appear explaining what the program is looking for. In this case the tool tip says "Select existing antenna file." Go ahead and click on the Open button, or alternately use the Alt-N keyboard combination. The standard Windows "common dialog" appears, from which you choose a file. See Fig 2.

Fig 2--The common dialog window for selecting a Yagi file. Let's start by opening up the 510-24H.YW file, which should be located in the default folder, and which is one of the 80+ Yagi designs included with The ARRL Antenna Book. As is standard Windows practice, double-click on the filename to open it, or single-click on it and select Open in the dialog box. Of course, you could also type in the file name, using either upper- or lowercase letters in the dialog box. After it opens the file, YW will convert to upper-case internally and display the file name under the Open button to remind you which file you've chosen. Once YW has loaded the data file, it computes the Gain, worst-case F/R and the SWR across the whole frequency band and generates an on-screen graph showing these three parameters. Look at the screen carefully -- there is a lot of information presented there. On the graph, the Gain is shown as a solid red line; F/R as a green line; and the SWR as a black line. Reference lines for the SWR readout are also displayed on the graph, with the 2:1 SWR limit shown as a thin violet line.

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You can see that the SWR curve for this antenna is higher than the 2:1 reference line all across the frequency range. Note also that below the graph is a table showing numerical readouts of the gain, F/R (front-to-rear ratio), Z (feed-point impedance) and 50- SWR for three discrete frequencies -- the bottom, middle and top of the frequency band. In this case the three frequencies shown are 28.000, 28.400 and 28.800 MHz. The SWR for this design in its native state is 3.37:1 at the bottom, 2.73:1 at the top, and 2.60:1 at the center of the band. You can "interrogate" each curve by moving the mouse cursor on it and reading out the numerical value at each plotted point. Let's try to match this Yagi better to a 50- coax feed line.

Fig 3--Gain, F/R and SWR curves for 510-24H Yagi over the 28.0-28.8 MHz band. Matching

Left-click on the Match button. A new form pops up, labeled Matching at the top left. You have a number of data readouts showing. Look at the data shown for the Feed-point Z. At the match frequency (which was automatically selected to be 28.4 MHz, although you can change it), the feed-point impedance is 28.3 ? j 30.4 ohms. The relative levels of the resistance and capacitive reactance give us a good clue here. Since the two are roughly equal in magnitude, this Yagi has been designed for a hairpin match, although a gamma match will work also.

Click on the option button labeled Hairpin at the top and some new information pops up at the bottom of the Matching form. The default Hairpin rod diameter is 0.25 inches and the

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default Hairpin rod spacing is 6 inches. These values approximate a Hy-Gain "beta" match, their name for a hairpin matching system. Let's use the default numbers for now, including the value of 50 ohms for the Cable Z0 impedance.

Click on the Compute Match button, which has turned yellow to alert you that a computation is needed. Some more new information appears, indicating that the Hairpin inductance should be 0.32 uH and the Hairpin length is 8.10 inches. You could implement an actual physical hairpin match by putting a 0.32 ?H coil across the driver feed-point terminals, or you could install a ?-inch diameter rod bent in the shape of a U, 6 inches wide by 8.10 inches long, across the feed-point terminals. Either way would work fine. See Fig 4.

Fig 4--Matching screen, where Hairpin has been chosen. Click on the OK button and YW will recompute across the band. Now the SWR curve falls below the 2:1 reference line, with a numerical readout of 1.64:1 at 28.0 MHz, 1.22:1 at 28.4 MHz and 1.23:1 at 28.8 MHz. These values aren't too bad. Now go back and try a gamma match. Click again on the Match button and then select Gamma and Compute Match. With the same ?-inch OD gamma rod and a spacing of 6" from the driver, YW computes that you need a 15.44-inch long gamma rod, in series with 45.8 pF. Click OK and look at the SWR curve again. Note that the SWR at the matching frequency of 28.4 MHz is exactly 1:1. This illustrates one of the advantages of a gamma match -- it gives a 1:1 SWR at the design frequency. A gamma match tends to be pretty broadband too. Now the SWR across the band is held lower than 1.31:1, very flat indeed.

Changing the Frequency Limits Let's see what happens if we change the frequency range for this 510-24H Yagi. Click on the Freq. button and a new form will pop up. Let's check out the response 400 kHz above and below

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the normal frequency limits of 28.0 and 28.8 MHz. The lower-frequency limit might simulate, for example, a situation where some ice accumulates on the elements. So, we type in 27.6 for the Low Frequency, MHz, and 29.2 for the High Frequency, MHz limits. Note that the form automatically computes the center frequency, which remains at 28.4 MHz for this case.

Fig 5--Setting the frequency limits. Now, the SWR curve at the low end of the range has gone to 2.28, but at the high-frequency end of the range the SWR has risen to 5.84. This Yagi design has been tailored to cover only the low end of the 28.0 to 29.7 MHz amateur band. Note that the F/R curve goes below 20 dB below about 27.9 MHz, while the gain remains reasonably flat both above and below the normal frequency range. Return to the normal frequency range by selecting Freq. and resetting the lower limit to 28.0 MHz and the high limit to 28.8 MHz. By the way, the easiest way to change a number in any of the data input boxes is by double-clicking the number. This highlights it so that you can overwrite the number easily by typing in new numbers.

Changing the Height Now, click on the Height button and after the new form appears type in a value, say, 60 feet. Complete your entry by clicking on the OK button.

Fig 6--Choosing a new height. At first glance, nothing much looks like it changed on the main graph. A closer look reveals that the gain figures have increased by almost 6 dB from their free-space values and a new label has appeared to the lower right side of the graph, indicating that the peak elevation angle is 8?. The height above ground has resulted in a gain increase at this elevation angle due to groundreflection gain. (See Chapter 3 in The ARRL Antenna Book.)

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Fig 7--Main window for 510-24H Yagi, 60 feet above flat ground.

If you wish to return to the default of free-space, you would type in a height of 0 feet. This automatically places the antenna in free-space. But before you reset yourself to free space, let's look at the details of the elevation pattern for our chosen height of 60 feet by using by using YW's plotting capabilities.

Changing the View

Click on the View button in the main window and you will be presented with a new form labeled View, other choices. The choices are broken down into three categories, separated inside outline frames: Units, Pattern and Graph. See Fig 8. We'll discuss the other choices later, but for now select ARRL polar plot and click on OK.

Fig 9 shows the free-space E-Plane and H-Plane patterns for the 510-24H 10-meter Yagi, mounted 60 feet above flat ground. Note that the responses are labeled "Az" (azimuth) and "El" (elevation), since the Earth is the reference plane. You can see that the 3-dB beamwidth in the Azimuth plane is 58? and only 8? in the Elevation plane.

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